Reverse sticker shadow

Q: Last week, I had a call from a customer with a concern about a load of 8/4 basswood that had white streaks wherever a sticker was located while the wood was being dried. They called this reverse sticker shadow. Can you help us with this problem?

A. Indeed, the correct term is reverse sticker shadow. The key to understanding the cause is that when drying lumber, differences in drying rates will often result in differences in color, especially with the white colored woods. Slower drying usually means slightly darker colors.

What has happened is that you apparently used very dry stickers on the basswood, so that resulted in very rapid drying right under the sticker, as the dry sticker sucked the moisture up in the area where the sticker contacted the lumber. This gives a nice white color. Then, for whatever reason (maybe humid outside conditions initially when air drying or a high humidity in the kiln initially), the wood between the stickers was dried more slowly and did not develop the desired white color. Avoid super dry stickers. Also, try to dry the wood aggressively (use a low humidity), especially the first few days.

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